Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2015

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Components Of Net Periodic Benefit Cost

The following table presents the components of the net periodic benefit cost (benefit) for Ameren’s pension and postretirement benefit plans for the three months ended March 31, 2015 and 2014:

	Pension Benefits						Postretirement Benefits
	Three Months							Three Months
	2015			2014				2015			2014
Service cost	$	24		$	21			$	5		$	5
Interest cost	44			49				12			13
Expected return on plan assets	(62		)	(57		)		(17		)	(16		)
Amortization of:
Prior service benefit	—			—				(1		)	(1		)
Actuarial loss (gain)	18			12				1			(1		)
Net periodic benefit cost	$	24		$	25			$	—		$	—

Summary Of Benefit Plan Costs Incurred

Ameren Missouri and Ameren Illinois are responsible for their respective shares of Ameren’s pension and postretirement costs. The following table presents the pension costs and the postretirement benefit costs incurred for the three months ended March 31, 2015 and 2014:

	Pension Benefits				Postretirement Benefits
	Three Months					Three Months
	2015		2014			2015			2014
Ameren Missouri	$	15	$	17		$	1		$	1
Ameren Illinois	9		8			(1		)	(1		)
Ameren(a)	$	24	$	25		$	—		$	—

(a) Includes amounts for Ameren registrants and nonregistrant subsidiaries.